A typical Business Communications customer in telecommunications, usually a large corporation, uses various types of communications services. These may include Switched Voice and Data, Packet, Frame Relay, Bandwidth-on-Demand, and Private Line Services.
Access configurations determining to which particular services a customer will have access at any time are currently fixed and maintained by a service provider, such as AT&T.
For switched voice applications, access circuits usually utilize a known robbed-bit signalling technique in which bits are "robbed" from a data stream and replaced with signalling information. Common types of robbed-bit signalling include Ground Start ("GS"); Loop Start ("LS"); Ear & Mouth ("E&M"); and Private Line Automatic Ringdown ("PLAR").
With the popularity of digital technology, voice (analog) signals from each phone line will usually undergo an analog-to-digital conversion by an electronic device such as a D4 channel bank employed by many Local and Inter-Exchange Carriers (such as AT&T). One voice channel, a DS0 channel, uses a bandwidth of 64 kbps (kilo-bits per second). Twenty-four DS0 channels are then combined, using the time division multiplexing technique, into a digital circuit or facility which is commonly called a "T1" (or alternatively "T1.5", or "DS1") access circuit (or alternatively "facility"). A single T1 facility thus has the capacity to carry 24 voice connections simultaneously or a combination of voice, dam, and video applications on those 24 DS0 channels. Since two-way communication is usually desired, each T1, which has a bandwidth of 1.544 Mbps (mega-bits per second), is a duplex facility capable of handling two-way data transmission at a rate of 1.544 Mbps in each direction.
The T1 facilities from customer sites are usually terminated on an electronic cross-connect device when they come into the Carrier Offices. On AT&T networks, this device is known as DACS-II (Digital Access and Cross-connect System - II, or simply "DACS"). A regular DACS can handle up to 640 T1 access facilities on 640 T1 duplex ports (one T1 facility per T1 port) and can be accessed and controlled remotely from a central point for providing DS0 connections to various network services offered by the telecommunications carrier. The digital cross-connect capability of DACS also permits assignment and redistribution of DS0 channels within and between the T1 facilities which terminate on it.
In a typical Carrier Office such as for AT&T, the DACS is connected to a variety of office equipment supporting the various network services provided. For example, there are connections to intelligent 4ESS.TM. switching systems for AT&T's Circuit Switched Services, to a 1PSS.TM. for AT&T's Packet Service, to an IPX/BPX for AT&T's Frame Relay service, and possibly to another DACS for AT&T's Private Line and Bandwidth-on-Demand services.
Connection to these, as well as to other, services is typically accomplished through internal mapping, or cross-connect, of the DS0 channels administrated at the DACS. Multiple services can share a single T1 access facility, however, the cross-connect maps associated with each particular service are currently fixed and maintained by individual servia.
DACS, with a Network Management System, has the capability to reconfigure (disconnect and connect or re-connect) the cross-connects between the access facilities and the connections to network services at the transmission level (i. e, at the physical layer of the known Open System Interconnection ("OSI") reference model). This reconfiguration capability of the DACS in a network environment is known as Reconfigurable Integrated Network Access ("RINA"). However, unresolved technical issues have been encountered at higher layers (again referring to OSI model). These issues include billing errors due to the inability to detect disconnected lines, where billing may continue indefinitely on the disconnected line after customer reconfiguration, and undesired or false alarms due to improper trunk conditioning. These difficulties, among others, have prevented the implementation of RINA in the past.
Static Integrated Network Access, or "SINA", is the arrangement that currently exists. For SINA, all cross-connects at the cross-connect system are fixed once the services as subscribed are turned up. SINA does not support and provides no capability to the customer for access reconfigurations.